Geologists just learned that the greatest extinction of life on Earth was aided and abetted by the burning of coal. Though this material has been a great boon for humans since the 18th century, it was a bane beyond measure for nearly every living thing during the 2,519,410th century B.C.

Why does this matter? Because the culprits of long ago were the same airborne pollutants the U.S. Environmental Protection Agency has been regulating for years. In the agency's fight against King Coal, it has slowed the pace toward planetary toxication.

Imagine a world where the rainfall was so acidic, that it drizzled from hazy skies with the pH of vinegar. Your eyes would sting with pain. According to a news report from last December's Science, such a world once existed, one where sulfuric acid killed much if not most terrestrial life. The source of that acid was sulfur dioxide leaking from fissure eruptions in Siberia so powerful that nothing could have stopped them. They covered an area almost half the size of the conterminous United States.

Imagine a world where the element mercury, a potent neurotoxin, fell from sooty skies with a concentration well above current safety levels. Given time, we'd all become mad as hatters. Such skies were common back then, when lava from the eruptions created what writer Richard Kerr called a "vast, subterranean, coal-fired inferno that belched metal-bearing ash into the stratosphere." Giga-tons of coal fly ash — just like that being regulated today at power plants — fell as dust contaminated with mercury, radionuclides and other toxic metals. Perhaps life on Earth went insane before it died from acid rain.

Imagine a world where the carbon dioxide pollution from that one-two punch of volcanic gas and combustion gas caused a rapid rise in temperature of at least 8 degrees centigrade. This exceeds by eight times what Earth has experienced since the Industrial Revolution, when the burning of fossil fuel began in earnest. It exceeds by a factor of four predictions for the peak warming to come later this century. Though this ancient warming came too late for the kill, it was abrupt enough to keep Earth's systems unstabilized.

The sequence is clear, based on recent investigations at Meishan, China, and precise dating by scientists at the Massachusetts Institute of Technology. Strike one was acid rain. Strike two was toxic fallout. Strike three was extinction of an estimated 90 percent of all species. Though the presence of these three events and the warming that followed have long been known, getting them in the right order had to await the discovery of the right geological site.

This nasty-beyond-nasty episode happened on the planet we call home. It should remind us that planet Earth is in charge, not us. As philosopher Will Durant so famously put it: "Civilization exists by geological consent, subject to change without notice."

Empowering environmental organizations to save us from ourselves is evidence that humans are brainy enough to adapt and survive. We've held SO2 emissions from coal-fired plants in check with enforceable regulations. We've also cut back on mercury contamination by insisting that smoke-stack scrubbers be installed. In fact, by 2016, EPA will have cut this airborne poison by more than 80 percent from 1990 levels. The U.S. is currently leading the way in global mercury containment, being the first nation to ratify the Minamata Convention on Mercury of the United Nations Environmental Program, named after the Japanese city where thousands of citizens were poisoned by this toxic element.

And now we're getting serious about cutting back on CO2 emissions from coal plants, though I wish it had been earlier.

The war is not yet over. SO2 emissions, fly-ash mercury and CO2 pollution are still major problems. Perhaps the recent recognition that these three substances contributed to life's greatest extinction can be taken as a sign that the environmental regulators have consistently been on the side of life, rather than death.

Robert M. Thorson is a professor at the University of Connecticut's College of Liberal Arts and Sciences. His column appears every other Thursday. He can be reached at profthorson@yahoo.com.